Electrical transformers typically include a primary winding and a secondary winding wound about a magnetic core. Energy from the primary winding transfers to the secondary winding through electromagnetic induction using the magnetic core.
In a conventional transformer, the primary winding is an electrically conductive wire such as a copper wire. A portion of the wire is in the form of a winding coil wound about the magnetic core with an amount of winding turns. Each winding turn of the winding coil is one loop of the wire. Similarly, the secondary winding is another wire and a portion of this wire is in the form of a winding coil wound about the magnetic core with an amount of winding turns.
In a planar transformer, the winding coils are flat, or planar, electrically conductive elements instead of wire loops. For instance, winding coils in certain planar transformers are spiral copper traces on a planar surface. In this type of planar transformer, a winding coil of the primary winding is a spiral of traces on a first board and a winding coil of the secondary winding is a spiral of traces on a second board.